The present disclosure relates to composite articles, in particular, a light weight, high strength composite article that is both temperature and water resistant.
It has been determined that it would be cost effective to utilize light weight, fire resistant composite articles in the construction of military vehicles, such as aircraft, ships, amphibious vehicles, and the like, as well as for structures. U.S. Pat. No. 4,936,939 to Woolum discloses a graphite fabric reinforced ceramic matrix composite material that has good mechanical and thermal characteristics. The '939 patent discloses a composite article that comprises alkali silicate with ceramic powder fillers that are manufactured and dried. The dried silicate composite article is placed in a treatment bath consisting of a soluble multivalent cation salt where the resulting combination of cation, cation salt, and pH result in an insoluble ceramic cation silicate binder matrix composite article. These conventional composite articles made of alkali silicates have passed dry strength and fire resistance tests, but lose integrity when exposed to moisture or water. The highly alkaline nature of the ions that remain in the composite article after formation will dissolve the silicates when exposed to moisture or water, resulting in the loss of integrity of the composite article. Since these conventional composite articles are not water resistant, they are not suitable for military vehicles or for exterior uses.
What is needed in the art is a post-treatment process that is simple, cost effective, and provides the necessary water resistance to composite articles rendering the composite articles light weight, high strength, resistant to high temperatures, able to pass fire rating tests and water resistant.